Magnetic recording medium and its manufacture

ABSTRACT

An inexpensive high-density recording medium which is increased in coercive force without using expensive ferromagnetic metallic layer. In a magnetic recording medium on the base body of which a ferromagnetic metallic layer is formed on a base body with a metallic underlying layer in between and which utilizes reversal of magnetization, the oxygen concentration in the ferromagnetic metallic layer is 100 wt. ppm or less, and in addition, oxygen concentration in the metallic base layer is also 100 wt. ppm or less. In a method of manufacturing a magnetic recording medium on the base body of which the metallic base layer and ferromagnetic metallic layer are successively formed by sputtering, the impurity concentration of Ar gas used for the formation of the layer is 10 ppb or less. Before forming the metallic base layer, in addition, the surface of the base body is cleaned by high-frequency sputtering using Ar gas the impurity concentration of which is 10 ppb and surface section of the base body is partially removed to a depth of 0.2-1 nm.

TECHNICAL FIELD

The present invention relates to a magnetic recording medium and amanufacturing method therefor. In greater detail, the present inventionrelates to a high density recording medium possessing superior magneticcharacteristics which is inexpensive and can be easily produced, as wellas to a manufacturing method therefor. The magnetic recording medium inaccordance with the present invention is preferably applied to harddisks, floppy disks, magnetic tape, and the like.

BACKGROUND ART

The following technology is known as a conventional magnetic recordingmedium and a manufacturing method therefor.

FIG. 23 is a schematic diagram showing a hard disk as an example of amagnetic recording medium. In FIG. 23, FIG. 23(a) is a perspective viewof the entirety of the magnetic recording medium, while FIG. 23(b) is across-sectional view of the section A-A' in FIG. 23(a).

A structure is employed in which a non-magnetic (Ni--P) layer 3 wasprovided on the surface of an Al substrate 2 which was employed as abase body 1. A Cr base layer 4, a ferromagnetic metallic layer 5, and aprotective layer 6 are laminated on this base body 1.

The non-magnetic (Ni--P) layer 3 is formed by means of a plating methodor a sputtering method on the surface of an Al substrate 2 which is inthe shape of a disk having a diameter of 89 mm (3.5 inch) and athickness of 1.27 mm (50 mil), and this forms the base body 1.Furthermore, concentric scratches (hereinbelow termed texture) areprovided in the surface of the non-magnetic (Ni--P) layer 3 by means ofa mechanical grinding process. Generally, the surface roughness of thenon-magnetic (Ni--P) layer 3, that is to say, the average center lineroughness Ra as measured in the radial direction, is within a range of 5nm-15 nm. Furthermore, the Cr base layer 4 and the ferromagneticmetallic layer 5 (generally, a Co alloy system magnetic film) are formedon the surface of the base body 1 by means of a plating method, a vapordeposition method, or a sputtering method, and finally, a protectivelayer comprising carbon or the like which serves to protect the surfaceof the ferromagnetic metallic layer 5 is provided by means of asputtering method. The typical thickness of each layer is as follows:the non-magnetic (Ni--P) layer 3 is within a range of 5 μm-15 μm, the Crbase layer 4 is within a range of 50 nm-150 nm, the ferromagneticmetallic layer is within range of 30 nm-100 nm, and the protective layer6 is within a range of 20 nm-50 nm.

In order to apply a high recording density to the medium describedabove, among the magnetic characteristics of the medium, it isparticularly necessary to increase the coercive force. Recently,customer requirements have been shifting from media having a coerciveforce within a range of 1200 Oe-1600 Oe to media having a coercive forceof 1800 Oe or more. The following technologies were known as methods forincreasing the coercive force in magnetic recording media which wereconventionally considered in order to respond to such needs.

1! Alterations in the composition of the ferromagnetic metallic layer

2! Making the crystalline grains of the ferromagnetic metallic layersmaller

3! Magnetically isolating the crystalline grains of the ferromagneticmetallic layer

However, the following problems were present in the conventionaltechnologies described above.

(1) Technology 1! has a large effect when, for example, Pt is includedin the ferromagnetic metallic layer. However, the costs thereof arehigh, and medium noise is also high, so that improvement is expected.With other materials, the effects of the film formation atmosphere arelikely to be felt, and it is difficult to realize a coercive force of1800 Oe or more.

(2) Technology 2! can be realized by reducing, for example, the filmthickness of the base layer; however, if the thickness is too greatlyreduced, the level of medium noise increases and this is not desirable.

(3) Technology 3! can be realized by utilizing dispersion of the base Crby means of, for example, high temperature heat processing after filmformation; however, the effects of gas emission within the filmformation chamber must be considered, and the like, so that theproduction process becomes complex, and this is undesirable.

The following technologies are known as manufacturing methods formagnetic recording media.

4! An increase in the base body surface temperature during filmformation

5! Regulation of base body potential

6! Regulation of film formation gas pressure However, the followingproblems were present in the conventional technologies described above.

(4) In technology 4!, an increase in the amount of gases emitted fromthe inside of the film formation chamber occurred, and production becameunstable, so that this was not desirable.

(5) Technology 5! exhibited no effects even at potentials greater thanthose conventionally employed, and there was a tendency for a number ofabnormal electrical discharges to occur, so that the film formationprocess was unstable, and this was not desirable.

(6) Technology 6! did not exhibit effects greater than thoseconventionally obtainable in the range in which discharge was possible(for example, 1 mTorr-30 mtorr).

The current state of (1) above is shown in Table 1. In the case in whichthe composition of the ferromagnetic metallic layer is altered, which isone method for increasing the coercive force, CoNiCr, CoCrTa, andCoCrPt, for example, are widely employed as the base alloys. Table 1shows the relative superiority or inferiority of these three alloys withrespect to various criteria. The number 1 in the table indicates themost superior of the three alloys.

                  TABLE 1                                                         ______________________________________                                        ITEM       CoNiCr       CoCrTa  CoCrPt                                        ______________________________________                                         1!Low cost                                                                              1            2       3                                              2!Relatively                                                                            2            3       1                                             uninfluenced                                                                  by film                                                                       formation                                                                     atmosphere                                                                     3!Higher  3            2       1                                             coercive force                                                                is facilitated                                                                (1800 Oe or                                                                   more)                                                                          4!Low level                                                                             3            1       2                                             of medium                                                                     noise                                                                          5!Normalized                                                                            2            1       2                                             coercive force                                                                (Hc/Hk.sup.grain) is                                                          high                                                                          ______________________________________                                    

That is to say, CoNiCr is superior with respect to low cost incomparison with the other materials; however, it possesses defects inthat there is an upper limit to the coercive force, and the level ofmedium noise is high. CoCrTa is superior in that the level of mediumnoise is low and the normalized coercive force is high. However, sinceit is liable to be affected by the film formation atmosphere, theconstruction necessary for large scale manufacturing processes isdifficult. CoCrPt is characteristic in that a higher coercive force canbe produced in comparison with the other materials. However, because therare metal Pt is employed, the cost is high, and there is also a problemin that the level of medium noise is high in comparison with that ofCoCrTa.

Accordingly, there has been a strong desire for the realization of amagnetic recording medium and a manufacturing method therefor which hasfeatures such that the material comprising the ferromagnetic metalliclayer is low in cost, a high coercive force of 1800 Oe or more can bemaintained, and the level of medium noise during recording and playbackis low.

The present invention has as an object thereof to provide a magneticrecording medium which realizes a high coercive force using a materialwhich does not contain Pt in the ferromagnetic metallic layer, thematerials of which are low in cost, which has a low level of mediumnoise, and the manufacturing process of which can be simplified.

Furthermore, the present invention has an object thereof to provide amanufacturing method for magnetic recording media which is capable ofproducing a medium having a high coercive force even when thetemperature of the base body surface during film formation is low, andwhich is capable of employing conventional base body potentials and filmformation gas pressures.

DISCLOSURE OF THE INVENTION

The present invention comprises a magnetic recording medium wherein aferromagnetic metallic layer is formed on the surface of a base bodywith a metallic base layer in between, and which employs reversal ofmagnetization, characterized in that the oxygen concentration in theferromagnetic metallic layer is less than or equal to 100 wtppm.

Furthermore, the magnetic recording medium in accordance with thepresent invention comprises a magnetic recording medium in which aferromagnetic metallic layer is formed on the surface of a base bodywith a metallic base layer in between, and which employs reversal ofmagnetization, characterized in that an oxygen concentration in themetallic base layer is 100 wtppm or less.

Furthermore, the magnetic recording medium in accordance with thepresent invention is characterized in that the oxygen concentration inthe ferromagnetic metallic layer is 100 wtppm or less.

Furthermore, the magnetic recording medium in accordance with thepresent invention comprises a magnetic recording medium, wherein aferromagnetic metallic layer is formed on the surface of a base body,which employs reversal of magnetization, characterized in that an oxygenconcentration in the ferromagnetic metallic layer is 100 wtppm or less.

The manufacturing method for magnetic recording media in accordance withthe present invention comprises a manufacturing method for magneticrecording media wherein a metallic base layer and a ferromagneticmetallic layer are successively formed by a sputtering method on thesurface of a base body, characterized in that the impurity concentrationof Ar gas used in film formation is 10 ppb or less. It is furtherpreferable that the impurity concentration of the Ar gas be 100 ppt orless.

The manufacturing method for magnetic recording media in accordance withthe present invention is characterized in that prior to forming themetallic base layer, the surface of the base body is subjected to acleaning process by means of a high frequency sputtering method using Argas having an impurity concentration of 10 ppb or less, and 0.2 nm-1 nmis removed.

The manufacturing method for magnetic recording media in accordance withthe present invention described above is effective even in the case inwhich the ferromagnetic metallic layer is formed directly on the surfaceof the base body.

Furthermore, the base body is characterized in that a non-magnetic layeris formed on the surface thereof.

In the manufacturing method for magnetic recording media in accordancewith the present invention, during the formation of the metallic baselayer and/or ferromagnetic metallic layer, a negative bias preferablywithin a range of -100 V--400 V is applied to the base body, and it isdesirable that the vacuum degree which is achieved be 8×10⁻⁸ Torr orless. It is further preferable that the surface temperature of the basebody be within a range of 60° C.-150° C.

The manufacturing method for magnetic recording media in accordance withthe present invention which is described above is effective even in thecase in which the surface roughness Ra of the base body is 3 nm or less.Furthermore, the method can also be applied to cases in which the gaswhich is used during the formation of the metallic base layer and/orferromagnetic metallic layer is (Ar+N₂) or (Ar+H₂).

Function

In the present invention, in a magnetic recording medium in which aferromagnetic metallic layer is formed on the surface of a base bodywith a metallic base layer in between, by keeping the oxygenconcentration in the ferromagnetic layer at 100 wtppm or lower, thereare few grains which have impurities as a nucleus thereof and whichprecipitate crystal growth, so that a uniform crystal grain can beobtained, and it is possible to realize a magnetic recording mediumhaving high coercive force in a direction parallel to the film surface.

Furthermore, in the present invention, in a magnetic recording medium inwhich a ferromagnetic layer is formed on the surface of a base body witha metallic base layer in between, the oxygen concentration of themetallic base layer, which comprises Cr and the like, is maintained at alevel of 100 wtppm or less, and thereby, good crystal growth is possibleeven when the film is thin. As a result, the degree of control of theoriented surfaces of the crystal grains comprising the ferromagneticmetallic layer (that is to say, the extent to which the C axis of thehcp structure lies in the film surface) increases, so that it ispossible to realize a magnetic recording medium having a high coerciveforce in a direction parallel to the film surface.

Furthermore, in the present invention, in a magnetic recording medium inwhich a ferromagnetic metallic layer is formed on the surface of a basebody with a metallic base layer in between, by means of maintaining theoxygen concentration in the ferromagnetic metallic layer and themetallic base layer at 100 wtppm or less, the non-magnetic Cr of themetallic base layer passes through the boundary between the two layersand is easily dispersed between the crystal grains of the ferromagneticmetallic layer without being affected by the impurities present in theferromagnetic metallic layer and the metallic base layer. As a result,the degree of magnetic isolation of each crystal grain of theferromagnetic metallic layer increases, so that it is possible torealize a magnetic recording medium having a high coercive force in adirection parallel to the film surface.

In the magnetic recording medium in accordance with the presentinvention, the thickness of the magnetic base layer is preferably withina range of 2.5 nm-100 nm, and is more preferably within a range of 5nm-30 nm, and thereby a high coercive force and a low level of mediumnoise can be simultaneously realized.

In the magnetic recording medium in accordance with the presentinvention, the thickness of the ferromagnetic metallic layer ispreferably within a range of 2.5nm-40 nm, and more preferably within arange of 5 nm-20 nm, and thereby, it is possible to realize a stillhigher coercive force.

Furthermore in the present invention, in a magnetic recording medium inwhich a ferromagnetic metallic layer is formed on the surface of a basebody, by means of maintaining the oxygen concentration in theferromagnetic metallic layer at 100 wtppm or less, there are few grainswhich have impurities as a nucleus thereof and which precipitate crystalgrowth, so that uniform crystal grains are obtainable even in thin filmregions of 30 nm or less, and it is possible to realize a magneticrecording medium having a high coercive force in a directionperpendicular to the film surface.

In the magnetic recording medium in accordance with the presentinvention, by means of maintaining the surface roughness Ra of the basebody preferably at level of 3 nm or less, and more preferably at a levelof 1 nm or less, it is possible to realize a still higher coerciveforce.

In the magnetic recording medium in accordance with the presentinvention, the normalized coercive force of the ferromagnetic metalliclayer (indicated by Hc/Hk^(grain)) is 0.3 or more and less than 0.5, sothat it is possible to realize a still lower level of medium noise.

In the magnetic recording medium in accordance with the presentinvention, Al alloy, glass, or silicon are preferably employed as thebase body material, since the surface roughness described above is thusrealizable at a low cost.

In the present invention, the magnetic recording medium is produced bysuccessively forming a metallic base layer and a ferromagnetic metalliclayer by means of a sputtering method on the surface of a base body;what is meant by "successively" is that after the formation of themetallic base layer, and until the formation of the ferromagneticmetallic layer on the surface thereof, the layer is not exposed to anatmosphere having a pressure equal to or greater than the gas pressureduring film formation. Using this meaning, by means of maintaining theimpurity concentration of the Ar gas which is used during the successiveformation of the metallic base layer and the ferromagnetic metalliclayer at a level of 10 ppb or less, and preferably at a level of 100 pptor less, it is possible to realize a manufacturing method for magneticrecording media which is capable of reducing the oxygen concentrationcontained in each layer described above.

Accordingly, the targets which are employed in the formation of themetallic base layer and ferromagnetic metallic layer contain amounts ofoxygen of, respectively, 150 ppm or less and 30 ppm or less, and inorder to maintain high purity of the atmosphere during film formation,it is desirable that the vacuum degree attained in the film formationchamber be 8×10⁻⁸ Torr or less.

Furthermore, in the present invention, prior to forming the magneticbase layer, the surface of the base body is subjected to a cleaningprocess by means of high frequency sputtering using Ar gas having animpurity Concentration of 10 ppb or less, and by means of extremelyshallow stripping to a depth of 0.2 nm-1 nm, it is possible to realize amanufacturing method for magnetic recording media having the followingtwo functions.

(1) It is possible to remove substances which adhere to the surface ofthe base body and which can not be removed by vacuum storage or heatprocessing, so that it is possible to promote the crystal growth of theCr film from the stage at which the Cr layer is thin (for example, 5 nm)As a result, even if a ferromagnetic metallic layer is formed on thethin Cr layer, it is possible to obtain a high coercive force parallelto the film surface.

(2) The dispersion of non-magnetic Cr from the Cr layer to the crystalgrain boundaries of the ferromagnetic metallic layer formed on the Crlayer is facilitated. As a result, each crystal grain forming theferromagnetic metallic layer becomes more resistant to magneticinteraction from adjoining crystal grains, and a high coercive force canbe obtained in a direction parallel to the film surface.

The above two functions, that is to say, the impurity concentration ofthe Ar gas and the cleaning processing with respect to the surface ofthe base body, exhibit identical effects even in the case in which aferromagnetic metallic layer is formed directly on the surface of thebase body.

The effect of the cleaning processing described above is exactlyopposite to the effect which would be predicted from etching by means ofa common sputtering method in magnetic recording media; this wasdiscovered for the first time by means of the present invention. That isto say, cleaning using a high frequency sputtering method with respectto the surface of the (Ni--P) layer which employed a common method wasintended to remove solely the surface region of the (Ni--P) layer, andthus to increase the adhesion strength of the thin film formed thereon,as disclosed in, for example, Japanese Patent Application, FirstPublication, No. Sho 64-70925, and the striping depth was as much as 1nm-20 nm. Moreover, it was disclosed that by means of this method, thecrystalline orientation of the Cr base layer which was formed wasaltered, and the coercive force of the medium was reduced. For thisreason, after the cleaning processing had been carried out, it wasnecessary to undertake an additional oxidation process which lastedanywhere from somewhat less than 100 seconds to a number of hours andwas complicated, so that productivity precipitously declined. Asdescribed above, the present invention makes it possible to mass producewith good productivity a magnetic recording medium having extremelysuperior magnetic characteristics, by means of executing a cleaningprocess removing 1 nm or less using Ar gas having a low impurityconcentration.

Furthermore, in the present invention, it is preferable that thecleaning rate when high frequency sputtering is used be within a rangeof 0.001 nm/sec-0.1 nm/sec; within this range, it is possible to stablyobtain a magnetic recording medium having a high coercive force.

Furthermore, when the metallic base layer and/or the ferromagneticmetallic layer is formed, the coercive force can be further increased byapplying a negative bias to the base body. It is particularly preferablethat this bias value be within a range of -100 V--400 V.

Furthermore, in the present invention, even when the surface temperatureof the base body during the formation of the metallic base layer and/orthe ferromagnetic metallic layer is within a range of 60° C.-150° C., itis possible to realize a coercive force which was conventionally onlyobtainable at temperatures of 250° C. or more. As a result,manufacturing can be conducted using a heating process at a lowertemperature than that which was conventionally employed. The amount ofgas released from the interior of the film formation chamber can bereduced, and plastics and the like which are susceptible to high heatmay also be employed as base body materials.

Embodiment Modes

Hereinbelow, embodiment modes of the present invention will beexplained.

(Base Body)

Examples of base bodies include, for example, aluminum, titanium oralloys thereof, silicon, glass, carbon, ceramics, plastics, resins, andcompound materials thereof, and base bodies in which a non-magnetic filmof a different substance has been coated on the surface of one of thesematerials by means of a sputtering method, a vapor deposition method, aplating method, or the like. It is preferable that the non-magnetic filmwhich is provided on the surface of the base body not be subject tomagnetization at high temperatures, be conductive, and be easilymechanically worked, while possessing the appropriate degree of surfacehardness. Especially preferable as a base body which fulfills suchconditions is a base body in which a (Ni--P) layer is provided as anon-magnetic film on the surface of an aluminum alloy.

With respect to the shape of the base body, for the purposes of use as adisk, a doughnut-shaped circular base body may be employed. A base bodyhaving the magnetized layers and the like described hereinbelow providedthereon, that is to say, a magnetic recording medium, is used whilebeing rotated at, for example, a speed of 3600 rpm about the center ofthe circular base body during magnetic recording and playback. At thistime, a magnetic head rides above the magnetic recording medium at aheight of approximately 0.1 μm. Accordingly, with regards to the basebody, it is necessary to appropriately control the surface flatness, theparallel nature of the front and back surfaces, undulation in thecircumferential direction of the base body, and the surface roughness.

Furthermore, when the base body is rotated or stopped, the surface ofthe magnetic recording medium and the magnetic head come into contactand rub against one another (Contact Start Stop, termed CSS). As acounter measure, there are cases in which concentric slight scratches(texture) are provided in the surface of the base body.

(Metallic Base Layer)

Examples of the metallic base layer include, for example, Cr, Ti, W andalloys thereof. When alloys are employed, combinations with, forexample, V, Nb, and Ta and the like are proposed. In particular, Cr iswidely employed in mass production, and the sputtering method and thevapor deposition method and the like are employed as film formationmethods.

The role of this metallic base layer is to promote crystal growth of theferromagnetic metallic layer so that, when the ferromagnetic metalliclayer comprising Co groups is provided on the metallic base layer, themagnetization easy axis of the ferromagnetic metallic layer lies along adirection within the base body surface; that is to say, the coerciveforce in a direction within the base body surface increases.

If a metallic base layer comprising Cr is produced by a sputteringmethod, then film growth factors controlling the crystalline naturethereof include, for example, the surface temperature of the base body,the gas pressure during film formation, the bias applied to the basebody, the thickness of the film formed, and the like. In particular, thecoercive force of the ferromagnetic metallic layer exhibits a tendencyto increase in proportion to the thickness of the Cr film, so that a Crfilm thickness within a range of 50 nm-150 nm is employed.

In order to increase the recording density, it is necessary to reducethe height at which the magnetic head rides above the surface of themedium. If the thickness of the Cr film described above is large, thereis a tendency for the surface roughness of the medium also to increase.Accordingly, it is desirable to realize a high coercive force using athin Cr film.

(Ferromagnetic Metallic Layer)

An example of the ferromagnetic metallic layer is, for example, a Cogroup alloy containing at least Co.

If the ferromagnetic metallic layer is provided on the surface of thebase body with a metallic base layer in between (that is to say, in thecase of a magnetic film for recording within the surface), examplesinclude, for example, CoNiCr, CoCrTa, CoPtCr, CoPtNi, CoNiCrTa,CoPtCrTa, and the like. In particular, CoNiCr has a low cost and isrelatively unaffected by the film formation atmosphere, CoCrTa has a lowlevel of medium noise, and the CoPt systems are capable of realizingcoercive forces of 1800 Oe or more, which are difficult to produce usingCoNiCr or CoCrTa, so that these are preferably employed. In order toincrease the recording density, and to reduce the manufacturing costs,the development of a ferromagnetic metallic layer having low materialcosts, a low level of medium noise, and which is capable of realizing ahigh coercive force, has been desired.

On the other hand, in the case in which the ferromagnetic metallic layeris provided directly on the surface of the base body without a metallicbase layer in between (that is to say, in the case of a magnetic layerused for perpendicular recording), examples include, for example, CoCr,CoPt, CoCrTa, and the like. Furthermore, there are cases in which a softmagnetic metallic layer is provided as a backing layer beneath theferromagnetic metallic layer. The establishment of materials andmanufacturing methods which, in such cases, make it possible to maintaina high coercive force in a direction perpendicular to the film surfaceeven when the ferromagnetic metallic layer is thin, have been desired.

(Magnetic Recording Medium Employing Reversal of Magnetization)

There are two types of magnetic recording medium which employ reversalof magnetization: a medium in which recording magnetization is formedparallel to the film surface of the ferromagnetic metallic layerdescribed above (in-surface magnetic recording medium) and a medium inwhich recording magnetization is formed perpendicularly (perpendicularmagnetic recording medium).

In both media, in order to increase the recording density, it isnecessary to provide for a further reduction in size of the recordingmagnetization. In this reduction in size, the leakage flux of eachrecording magnetization is reduced, so that the playback signal outputin the magnetic head is reduced in size. Accordingly, a furtherreduction in the level of magnetic noise, which is thought to resultfrom the influence of adjacent recording magnetizations, is desired.

(Oxygen Concentration in the Ferromagnetic Metallic Layer)

It is known that the oxygen concentration in the ferromagnetic metalliclayer, for example, in the case of a CoNiCr film produced by means ofthe conventional sputtering method, is 250 wtppm or more. Researchrelated to the effect of the oxygen concentration in the ferromagneticmetallic layer, that is to say, the influence with respect to thecoercive force of the medium or the medium noise, has been desired.

What is meant by the conventional sputtering method described above isfilm formation under conditions such that the vacuum degree attainedwithin the film formation chamber in which the ferromagnetic metalliclayer is formed is within a range of 1×10⁻⁷ -5×10⁻⁷ Torr, and theimpurity concentration of the Ar gas used when forming the ferromagneticmetallic layer is 1 ppm or more.

(Oxygen Concentration in the Metallic Base Layer)

With respect to the oxygen concentration in the metallic base layer, itis known that, for example, in the case of the Cr film produced by meansof the conventional sputtering method, this concentration is 250 wtppmor more. Investigations with respect to the influence of the oxygenconcentration in the metallic base layer, that is to say, the influenceon the crystal growth process depending on the thickness of the metallicbase layer, the influence on the ferromagnetic metallic layer formed onthe metallic base layer, and the like, have been desired.

The meaning of the conventional sputtering method described above isidentical to that given under the heading "Oxygen Concentration in theFerromagnetic Metallic Layer" above.

(Normalized Coercive Force of the Ferromagnetic Metallic Layer(indicated by Hc/Hk^(grain)))

What is meant by the normalized coercive force of the ferromagneticmetallic layer is the value resulting when the coercive force Hc isdivided by the anisotropic field Hk^(grain) of the crystal grain, andthis value expresses the extent to which the magnetic isolation of thecrystal grains increases; this is disclosed in "Magnetization ReversalMechanism Evaluated by Rotational Hysteresis Loss Analysis for the ThinFilm Media," Migaku Takahashi, T. Shimatsu, M. Suekane, M. Miyamura, K.Yamaguchi and H. Yamasaki: IEEE TRANSACTIONS ON MAGUNETICS, VOL. 28,1992, pp. 3285.

The normalized coercive force of ferromagnetic metallic layers producedby a conventional sputtering method was smaller than 0.3, insofar as theferromagnetic metallic layers comprised Co groups. In accordance withthe Stoner-Wohlfarth theory, when the crystal grains are completelymagnetically isolated, a value of 0.5 is indicated, and this valuerepresents the upper limit of the normalized coercive force.

Furthermore, in J. -G. Zhu and H. N. Bertram: Journal of AppliedPhysics, VOL. 63, 1988, pp. 3248, it is stated that when the normalizedcoercive force of the ferromagnetic metallic layer is high, the magneticinteraction of the various crystal grains comprising the ferromagneticmetallic layer is reduced, and it is possible to realize a high coerciveforce.

Here, what is meant by coercive force Hc is the coercive force of themedium obtained from the magnetization curve measured using a variablesample magnetometer (termed VSM). The anisotropic field Hk^(grain) ofthe crystal grain indicates the applied magnetic field at which therotational hysteresis loss measured using a highly sensitive torquemagnetometer completely disappears. The coercive force and theanisotropic field represent values measured within the plane of the filmsurface in the case of a magnetic recording medium in which aferromagnetic metallic layer is formed on the surface of a base bodywith a metallic base layer in between, and represent values measured ina direction perpendicular to the film surface in the case of a magneticrecording medium in which a ferromagnetic metallic layer is formed onthe surface of a base body.

(Aluminum Alloy)

Examples of an aluminum alloy include, for example, an alloy comprisingaluminum and magnesium. Presently, disks employing an aluminum alloy asa base body are the most widely employed in HD (hard disk) uses. Sincethe purpose of use is magnetic recording, it is preferable that littlemetallic oxide be contained.

Furthermore, there are a number of cases in which a (Ni--P) film, whichis non-magnetic, is provided on the surface of the aluminum alloy bymeans of a plating method or sputtering method. The purpose of this isto increase corrosion resistance and to increase the surface hardness ofthe base body. In order to reduce the frictional force produced when themagnetic head rubs against the surface of the medium, slight concentricscratches (texture) are provided in the surface of this (Ni--P) film.

The problems involved in the case in which an aluminum alloy is used asthe base body are making the base body thin and reducing the surfaceroughness of the base body. Currently, the former has a limit of 0.5 mm,while the latter has a limit of approximately 0.5 nm.

(Glass)

Examples of the glass include, for example, glass which has beenstrengthened by means of conducting iron doping with respect to theglass surface, glass in which the glass itself comprises amicrocrystalline structure, and the like. Both have thus been treated soas to eliminate the drawback of glass, that it is easy to break.

The surface hardness of glass is high in comparison with that ofaluminum alloy, so that glass is superior in that it is not necessary toprovide a (Ni--P) film or the like; furthermore, it is also advantageousfrom the point of view of the thinning of the base body, the smoothingof the base body surface, and the high temperature resistancecharacteristics of the base body.

However, in order to produce a magnetic film having a high coerciveforce, it is preferable to set the surface temperature of the base bodyduring film formation to a high temperature and to conduct filmformation while applying a bias with respect to the base body, so thatthere are cases in which a non-magnetic layer is provided on the surfaceof the glass. Furthermore, in order to prevent the entry of harmfulelements from the glass into the magnetic film, there are cases in whicha non-magnetic layer is disposed. Alternatively, there are cases inwhich, in order to reduce the frictional force when the magnetic headrubs against the base body surface, a non-magnetic layer having a fineirregular surface is disposed on the surface of the glass.

The problems to be solved when glass is used as the base body are thethinning of the base body and techniques to prevent base body breakage.

(Silicon)

Examples of silicon include, for example, silicon wafers, which have ahistory of use in the semiconductor field, which are formed into a discshape.

As with glass, the surface hardness of silicon is high, and the thinningof the base body is possible; the smoothness of the base body is alsohigh, and the high temperature resistance characteristics of the basebody are good, so that silicon is superior to aluminum alloy. Inaddition, the crystal orientation and the lattice constant of the basebody surface can be selected, so that an improvement in thecontrollability of the crystal growth of the magnetic film formedthereon is expected. Furthermore, as with the aluminum alloy, the basebody possesses conductivity, so that it is possible to apply a bias tothe base body, and emission of gases such as H₂ O and the like from theinterior of the base body is small, so that this is advantageous fromthe point of view of achieving greater cleanliness in the film formationareas.

The problems to be solved in the case in which silicon is employed asthe base body are, as in the case of glass, the thinning of the basebody and techniques for preventing the breakage of the base body.

(Sputtering Method)

Examples of the sputtering method include, for example, the conveyedtype, in which a thin film is formed while moving the base body in frontof the target, and the stationary type, in which the base body is fixedin front of the target and a thin film is formed. Since the productivityof the former is high, it is advantageous for low cost production ofmedia, while with the latter type, the angle of incidence of thesputtered grain with respect to the base body is stable, so that it ispossible to manufacture base bodies which have superior recording andplayback characteristics.

(Successive Formation of the Metallic Base Layer and the FerromagneticMetallic Layer)

What is meant by the successive formation of the metallic base layer andthe ferromagnetic metallic layer is that "after the formation of themetallic base layer on the surface of the base body, and until theformation of the ferromagnetic metallic layer on the surface thereof,the surface is not exposed to an atmosphere having a pressure equal toor higher than the gas pressure during film formation." It is known thatwhen a ferromagnetic metallic layer is formed on the surface of themetallic base layer after the surface has been exposed to theatmosphere, the coercive force of the medium declines precipitously (forexample, from 1500 Oe without exposure to 500 Oe or less when exposed).

(Impurities Present in the Ar Gas Used in Film Formation and theConcentration Thereof)

Examples of impurities which are present in the Ar gas used in filmformation include, for example, H₂ O, O₂, CO₂, H₂, N₂, C_(x) H_(y), andthe like. The impurities which particularly influence the amount ofoxygen incorporated in the film are thought to be H₂ O, O₂, and CO₂.Accordingly, the impurity concentration in the present invention will beexpressed as the sum of the H₂ O, O₂, and CO₂ contained in the Ar gaswhich is used in film formation.

(Cleaning Processing by a High Frequency Sputtering Method)

Examples of cleaning processing by means of a high frequency sputteringmethod include, for example, the method in which an alternating voltagefrom a RF (radio frequency, 13.56 MHZ) power source is applied to a basebody which is placed within an area having a gas pressure permittingdischarge. The advantage of this method is that it can also be appliedin cases in which the base body is non-conductive. In general, theeffect of cleaning processing is to increase the ability of the thinfilm to adhere closely to the base body. However, there are many unclearpoints with respect to the effects on the film quality of the thin filmitself which is formed on the surface of the base body after cleaningprocessing.

(Impurities in the Cr Target Used During the Formation of the MetallicBase Layer and the Concentration Thereof)

Examples of impurities in the Cr target used during the formation of themetallic base layer include, for example, Fe, Si, Al, C, O, N, H, andthe like. The impurity which is thought to particularly effect theamount of oxygen incorporated into the film is O. Accordingly, theimpurity concentration in the present invention is indicated by theoxygen contained in the Cr target which is used during the formation ofthe metallic base layer.

(Impurities in the Target Used During the Formation of the FerromagneticMetallic Layer and the Concentration Thereof)

Examples of impurities in the Co group target used during the formationof the ferromagnetic metallic layer include, for example, Fe, Si, Al, C,O, N, and the like. The impurity which is thought to particularly affectthe amount of oxygen incorporated into the film is O. Accordingly, theimpurity concentration in the present invention is indicated by theoxygen contained in the target used during the formation of theferromagnetic metallic layer.

(Application of a Negative Bias to the Base Body)

The application of a negative bias to the base body indicates theapplication of a direct current bias voltage with respect to the basebody during the formation of a Cr base film or a magnetic film as amagnetic recording medium. It is known that if an appropriate biasvoltage is applied, the coercive force of the medium is increased. It iscommonly known that the effect of the bias application described aboveis greater when a bias is applied in the case of both layers than in thecase in which the bias is applied during the execution of only one orthe other of the layers.

(Vacuum Degree Attained in the Film Formation Chamber in which theMetallic Base Layer and/or the Ferromagnetic Metallic Layer is Formed)

The vacuum degree attained in the film formation chamber in which themetallic base layer and/or ferromagnetic metallic base layer is formedis one film growth factor affecting the value of the coercive force,depending on the material of the ferromagnetic metallic layer. Inparticular, when Co group material in which Ta is contained in theferromagnetic metallic layer is used, the effect is large when thevacuum degree attained is low (for example, in the case of a vacuumdegree of 5×10⁻⁶ Torr or more).

(Surface Temperature of the Base Body During the Formation of theMetallic Base Layer and/or the Ferromagnetic Metallic Layer)

The surface temperature of the base body during the formation of themetallic base layer and/or the ferromagnetic metallic layer is one filmgrowth factor which affects the value of the coercive forceindependently of the material of the ferromagnetic metallic layer. Thehigher the surface temperature at which film formation is conducted, thehigher the coercive force which can be realized, within such a rangethat the base body is not damaged. What is meant by damage to the basebody is external changes such as warping, swelling, cracking, or thelike, and internal changes, such as magnetization, an increase in theamount of gas emitted, and the like.

(Surface Roughness Ra of the Base Body)

Examples of the surface roughness of the base body include, for example,the average center line roughness Ra in the case in which the surface ofa disc shaped base body is measured in a radial direction. The TALYSTEPproduced by RANKTAYLORHOBSON Co. was used as the measuring instrument.

When base body rotation is initiated from a stopped state, or viceversa, the surfaces of the magnetic recording medium and the magnetichead come into contact and rub against one another (Contact Start Stop,termed CSS). At this time, in order to suppress the adhesion of themagnetic head and an increase in the coefficient of friction, ispreferable that Ra be large. On the other hand, when the maximumrotational frequency of the base body is reached, it is necessary tomaintain a gap between the magnetic recording medium and the magnetichead, that is to say, to maintain the distance at which the magnetichead rides above the medium, so that it is desirable that Ra be small.

Accordingly, the maximum and minimum values of the surface roughness Raof the base body are appropriately determined from the specificationsrequired with respect to the magnetic recording medium, for the reasonsdescribed above. For example, when the height at which the magnetic headrides above the medium is 2 μinch, Ra should be within a range of 6 nm-8nm.

(Texture Processing)

Examples of texture processing include, for example a method employingmechanical grinding, a method employing chemical etching, and a methodemploying the provision of a physically irregular film. In particular,when an aluminum alloy base body, which is most widely employed, is usedas the base body of the magnetic recording medium, a mechanical grindingmethod is adopted. For example, a method is employed in which tape,having on the surface thereof abrasive grain used for grinding, isapplied to the (Ni--P) film provided on the surface of an aluminum alloybase body while this base body is rotating, and thereby slightconcentric scratches are created. When using this method, there arecases in which the abrasive grain used for grinding is employed so as tobe free of the tape.

(Composite Electrolytic Polishing Processing)

Examples of composite electrolytic polishing processing include, forexample, processing which provides an oxide passivated film, havingchromium oxide as a product thereof, on the inner walls of a vacuumchamber used during the formation of a magnetic film or the like. Inthis case, SUS316L or the like is preferable for use as the materialcomprising the inner walls of the vacuum chamber. By means of thisprocessing, the amount of O₂ and H₂ O released from the inner walls ofthe vacuum chamber can be reduced, so that it is possible to furtherreduce the amount of oxygen incorporated into the thin film which isproduced.

In the magnetron sputtering apparatus (model number ILC3013: load-lockstyle stationary opposition type) produced by Aneruba Co. which was usedin the present invention, the inner walls of all the vacuum chambers(the load/extraction chamber, the film formation chambers, and thecleaning chamber) were subjected to the processing described above.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing the relationship between the oxygenconcentration in a CoNiCr film in accordance with Embodiment 1 and thecoercive force of the medium produced.

FIG. 2 is an image of the surface of a magnetic recording medium takenby a transmission electron microscope (TEM).

FIG. 3 is an image of the surface of a magnetic recording medium takenby a transmission electron microscope (TEM).

FIG. 4 is a graph showing the relationship between the oxygenconcentration in a Cr film in accordance with Embodiment 2 and thecoercive force of the medium produced.

FIG. 5 is a graph showing the relationship between the oxygenconcentration present in a CoNiCr film in accordance with Embodiment 3and the coercive force of the medium produced, with respect to theoxygen concentration present in the Cr film.

FIG. 6 is a graph showing the relationship between the film thickness ofa metallic base layer comprising Cr in accordance with Embodiment 5 andthe coercive force of the medium produced.

FIG. 7 is a graph showing the relationship between the film thickness ofa metallic base layer comprising Cr in accordance with Embodiment 5 andthe noise Nm of the medium produced.

FIG. 8 is a graph showing the relationship between the film thickness ofa metallic base layer comprising CoCrTa in accordance with Embodiment 6and the coercive force of the medium produced.

FIG. 9 is a graph showing the relationship between the oxygenconcentration present in a CoNiCr film in accordance with Embodiment 7and the coercive force of the medium produced.

FIG. 10 is a graph showing the relationship between the normalizedcoercive force (Hc/Hk^(grain)) in accordance with Embodiment 8 and thenoise (Nm) of the medium produced.

FIG. 11 is a graph showing the relationship between the impurityconcentration present in the Ar gas used during the formation of aferromagnetic metallic layer and a metallic base layer in accordancewith Embodiment 9, and the coercive force of the medium produced.

FIG. 12 is a graph showing the relationship between the amount ofstripping of the base body surface carried out by the cleaningprocessing in accordance with Embodiment 10, and the coercive force ofthe medium produced.

FIG. 13 is a graph showing the results of the X-ray diffraction of thesurface of a medium in accordance with Embodiment 10.

FIG. 14 is a graph showing the relationship between the impurityconcentration of the target used during the formation of a metallic baselayer in accordance with Embodiment 11 and the coercive force of themedium produced.

FIG. 15 is a graph showing the relationship between the impurityconcentration of a target used during the formation of a ferromagneticmetallic layer in accordance with Embodiment 12, and the coercive forceof the medium produced.

FIG. 16 is a graph showing the relationship between the negative biasvalue applied to the base body in accordance with Embodiment 13 and thecoercive force of the medium produced.

FIG. 17 is a graph showing the relationship between the vacuum degreeattained in the film formation chambers in which a metallic base layerand a ferromagnetic metallic layer in accordance with Embodiment 14 areformed, and the coercive force of the medium produced.

FIG. 18 is a graph showing the relationship between the surfacetemperature of the base body during the formation of a base metalliclayer and/or a ferromagnetic metallic layer in accordance withEmbodiment 15, and the coercive force of the medium produced.

FIG. 19 is a graph showing the relationship between the surfacetemperature of the base body during the formation of a metallic baselayer and/or a ferromagnetic metallic layer in accordance withEmbodiment 15, and the surface roughness Ra of the medium produced.

FIG. 20 is a graph showing the relationship between the surfaceroughness Ra of a base body in accordance with Embodiment 16, and thecoercive force of the medium produced.

FIG. 21 is a graph showing the relationship between the proportion ofthe N₂ gas in the (Ar+N₂) gas in accordance with Embodiment 17 and thecoercive force of the medium produced.

FIG. 22 is a graph showing the relationship between the proportion of H₂gas in the (Ar+H₂) gas in accordance with Embodiment 17 and the coerciveforce of the medium produced.

FIG. 23 is a schematic view showing a magnetic recording medium.

(Description of the References)

1. Al substrate,

2. magnetic (Ni--P) layer,

3. Cr base layer,

4. ferromagnetic metallic layer,

5. protective film.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinbelow, the present invention will be explained in detail usingEmbodiments; however, the present invention is no way limited to theseEmbodiments.

(Embodiment 1)

In the present Embodiment, the effects of limiting the oxygenconcentration contained in the ferromagnetic metallic layer in amagnetic recording medium in which a ferromagnetic metallic layer isformed on the surface of a base body with a metallic base layer inbetween will be explained. In order to confirm these effects, filmformation was conducted while varying the impurity concentrationcontained in the Ar gas during the formation of the ferromagneticmetallic layer within a range of 10 ppb-1 ppm. At this time, theimpurity concentration contained in the Ar gas during formation of themetallic base layer was fixed at 1 ppm.

The sputtering apparatus which was used in producing the medium in thepresent Embodiment was a magnetron sputtering apparatus (model numberILC3013: load-lock style stationary opposition type) produced by AnerubaCo., and the inner walls of all the vacuum chambers (the load/extractionchamber (combined with the cleaning chamber), film formation chamber 1,film formation chamber 2, and film formation chamber 3) were subjectedto composite electrolytic polishing processing. Table 1 shows the filmformation conditions during the execution of the magnetic recordingmedia of the present invention.

                  TABLE 2                                                         ______________________________________                                        ITEM              SET VALUES                                                  ______________________________________                                         1! Base Body material                                                                          Al-Mg alloy (provided with a                                                  10 μm thick (Ni-P) plated film)                           2! Base Body diameter and                                                                      89 mm, disc-shaped                                          shape                                                                          3! Base Body surface form                                                                      Textured, Ra = 5 nm                                          4! Attained vacuum degree                                                                      5 × 10.sup.-7 (same in all chambers)                  (Torr)                                                                         5! Impurity concentration in                                                                   10 ppb - 1 ppm (film formation                              the Ar gas        chamber 2)                                                                    1 ppm (other than film                                                        formation chamber 2)                                         6! Ar gas pressure (mTorr)                                                                     2 (same in all chambers)                                     7! Base Body surface                                                                           250 (same in all chambers)                                  temperature maintained (°C.)                                            8! Target material (at %)                                                                      Cr, Co.sub.62.5 Ni.sub.30 Cr.sub.7.5, C                      9! Target diameter (inch)                                                                      6                                                            10! Impurity concentration in                                                                  120 (Cr), 20 (CoNiCr)                                       target (ppm)                                                                   11! Distance between target                                                                    35 (Cr, CoNiCr, C)                                          and base body (mm)                                                             12! Power applied to target                                                                    Direct current, 200 (Cr,                                    (W)               CoNiCr)                                                                       Direct current, 400 (C)                                      13! Direct current bias                                                                        200 (Cr), 300 (CoNiCr), 0 (C)                               applied to base body during                                                   film formation (-Volt)                                                         14! Film thickness produced                                                                    50 (Cr), 40 (CoNiCr), 20 (C)                                (nm)                                                                          ______________________________________                                    

Hereinbelow, the production method for magnetic recording media inaccordance with the present Embodiment will be explained in order of theprocesses involved. The numbers in parentheses below indicate thisorder.

(1) An aluminum alloy base body having a disk shape, such that the innerand outer radiuses were 25 mm and 89 mm and the thickness was 1.27 mm,was used as a base body. An (Ni--P) film having a thickness of 10 μm wasprovided by means of a plating method on the surface of the aluminumalloy substrate. Slight concentric scratches (texture) were provided onthe surface of the (Ni--P) film by means of a mechanical method, and thesurface roughness of the base body when scanned in the radial directionof the disk was such that the average center line roughness Ra was 5 nm.

(2) The base body described above was subjected, prior to the filmformation described hereinbelow, to a cleaning process by means ofmechanical and chemical methods, and a drying process using hot air andthe like.

(3) After the completion of the drying process described above, thematerial was set in a base body holder comprising aluminum which wasplaced in the load chamber of the sputtering apparatus. After theinterior of the load chamber was evacuated to an attained vacuum degreeof 1×10⁻⁷ Torr by means of a vacuum exhaust apparatus, the base body wassubjected to a heating process using an infrared lamp at a temperatureof 250° C. and for a period of five minutes.

(4) The base body holder described above was moved from the load chamberto the film formation chamber 1 for Cr film production. After beingmoved, the base body was maintained at a temperature of 250° C. using aninfrared lamp. However, the film formation chamber 1 was evacuated inadvance to an attained vacuum degree of 3×10⁻⁹ Torr, and after movingthe base body holder, the door valve between the load chamber and filmformation chamber 1 was closed. The impurity concentration of the Crtarget which was employed was 120 ppm.

(5) Ar gas was introduced into film formation chamber 1, and the gaspressure of film formation chamber 1 was set to 2 mTorr. The impurityconcentration contained in the Ar gas which was used was fixed at 1 ppm.

(6) A voltage of 200 W was applied to the Cr target from a directcurrent power source and a plasma was generated. As a result, the Crtarget was caused to sputter, and a Cr layer having a thickness of 50 nmwas formed on the surface of the base body which was in a position ofparallel opposition to the target.

(7) After forming the Cr layer, the base body holder was moved from filmformation chamber 1 to the film formation chamber 2 for CoNiCr filmproduction. After being moved, the base body was maintained at atemperature of 250° C. by means of an infrared lamp. Film formationchamber 2 was evacuated to an attained vacuum degree of 3×10⁻⁹ Torr, andafter the base body holder was moved, the door valve between filmformation chamber 1 and film formation chamber 2 was closed. The targetcomposition which was used was 62.5 at % Co, 30 at % Ni, and 7.5 at %Cr, and the impurity concentration of the target was 20 ppm.

(8) Ar gas was introduced into film formation chamber 2 and the gaspressure of film formation chamber 2 was set to 2 mTorr. The impurityconcentration contained in the Ar gas which was employed was variedwithin a range of 10 ppb-1 ppm.

(9) A voltage of 200 W was applied to the CoNiCr target from a directcurrent power source, and a plasma was generated. As a result, theCoNiCr target was caused to sputter, and a CoNiCr layer having athickness of 40 nm was formed on the surface of the base body coatedwith a Cr layer, which was in a position of parallel opposition to thetarget.

(10) After the CoNiCr layer was formed, the base body holder was movedfrom film formation chamber 2 to film formation chamber 3 for C filmproduction. After being moved, the base body was maintained at atemperature of 250° C. by means of an infrared lamp. Film formationchamber 3 was evacuated in advance to an attained vacuum degree of3×10⁻⁹ Torr, and after the base body holder was moved, the door valvebetween film formation chamber 2 and film formation chamber 3 wasclosed.

(11) Ar gas was introduced into film formation chamber 3, and the gaspressure in film formation chamber 3 was set to 2 mTorr. The impurityconcentration contained in the Ar gas which was employed was fixed at 1ppm.

(12) A voltage of 400 W was applied to the C target from a directcurrent power source and a plasma was generated. As a result, the Ctarget was caused to sputter, and a C layer having a thickness of 20 nmwas formed on the surface of the base body, which was provided with aCoNiCr and a Cr layer, and which was in a position of parallelopposition to the target.

(13) After the C layer was formed, the base body holder was moved fromfilm formation chamber 3 to the extraction chamber. After this, N₂ gaswas introduced into the extraction chamber, and after the pressure wasreturned to atmospheric pressure, the base body was removed. By means ofprocesses (1)-(12) described above, a magnetic recording medium having aC/CoNiCr/Cr/NiP/Al structure was produced.

Targets were employed in which the presence of impurities was strictlysuppressed. The amounts of impurities in the target used for Crformation were as follows: Fe:88, Si:34, Al;10, C:60, O:120, N:60, H:1.1(wtppm). Furthermore, the composition of the target used forferromagnetic metallic layer formation was Ni:29.2 at %, Cr:7.3 at %,and Co: bal. The impurities were as follows: Fe:27, Si<10, Al<10, C:30,O:20, and N>10 (wtppm).

In FIG. 1, the magnetic characteristics of the medium which was producedare indicated by a white circle. The horizontal axis in FIG. 1 indicatesthe oxygen concentration in the CoNiCr film. The measurement of thisoxygen concentration was conducted by means of SIMS. The vertical axisin FIG. 1 indicates the coercive force Hc in the circumferentialdirection of the sample at this time.

Conventionally, the impurity concentration present in the Ar gas whichwas employed during the formation of a ferromagnetic metallic layercomprising CoNiCr was 1 ppm. Furthermore, the oxygen concentrationpresent in the CoNiCr layer in a conventional medium was 260 wtppm, andthe coercive force of a conventional medium is indicated in FIG. 1 by ablack circle.

In the present Embodiment, as shown in FIG. 1, by maintaining the oxygenconcentration present in the CoNiCr film at a level of 100 wtppm orbelow, the coercive force increased dramatically, and a level of 90wtppm or below was particularly advantageous. It was separately observedthat the saturation magnetization values at this time were essentiallyconstant.

FIGS. 2 and 3 are images of the surfaces of the various media describedabove taken using a transmission electron microscope (TEM); FIG. 2 showsthe case in which the oxygen concentration in the film was 90 wtppm,while FIG. 3 indicates the case in which the oxygen concentration was140 wtppm. It was determined that in the film shown in FIG. 2, thegrains were uniform and a fine film was obtained, while in FIG. 3, theoutlines of the crystals were unclear.

Accordingly, it was judged that if the oxygen concentration in theferromagnetic metallic layer was held at a level of 100 wtppm or less,the coercive force obtained in the case in which the oxygenconcentration present in a conventional ferromagnetic metallic layercomprising CoNiCr was 260 wtppm could be increased by 50% or more. Thatis to say, even if Pt was not contained in the magnetic layer, byreducing the oxygen concentration in the ferromagnetic metallic layer,it was possible to realize a medium applicable to high recordingdensities.

(Embodiment 2)

In the present Embodiment, the effects of a limitation of the oxygenconcentration contained in the metallic base layer in a magneticrecording medium in which a ferromagnetic metallic layer is formed onthe surface of a base body with a metallic base layer in between will bediscussed. In order to confirm these effects, the impurity concentrationcontained in the Ar gas during the formation of the metallic base layerwas varied within a range of 10 ppb-1 ppm and film formation wasconducted. At this time, the impurity concentration contained in the Argas during formation of the ferromagnetic metallic layer was fixed at 1ppm.

Other points were identical to those in Embodiment 1.

In FIG. 4, the magnetic characteristics of the media obtained areindicated by white circles. The horizontal axis in FIG. 4 indicates theoxygen concentration present in the Cr film. The measurement of theoxygen concentration was conducted by means of SIMS. In FIG. 2, thevertical axis indicates the coercive force Hc in the circumferentialdirection of the sample at this time.

Conventionally, the impurity concentration present in the Ar gas whichwas employed during formation of the metallic base layer comprising Crwas 1 ppm. Furthermore, the oxygen concentration in the Cr film in aconventional medium was 260 wtppm and the coercive force of theconventional medium is indicated in FIG. 4 by the black circles.

In the present Embodiment, as shown in FIG. 4, by means of keeping theoxygen concentration present in the Cr film at a level of 100 wtppm orless, an effect was obtained of an increase in the coercive force. Itwas separately observed that the saturation magnetization values at thistime were essentially constant.

Accordingly, it was judged that by keeping the oxygen concentrationpresent in the magnetic base layer at a level of 100 wtppm or less, thecoercive force obtained in the case in which the oxygen concentration ina conventional metallic base layer comprising Cr was 260 wtppm could beincreased by 30% or more. That is to say, even though no Pt wascontained in the magnetic layer, by reducing the oxygen concentration inthe metallic base layer, it was confirmed that a medium applicable tohigh recording densities could be realized.

(Embodiment 3)

In the present Embodiment, the effects of a limitation of the oxygenconcentration contained in the ferromagnetic metallic layer and theoxygen concentration contained in the metallic base layer in a magneticrecording medium in which a ferromagnetic metallic layer is formed onthe surface of the base body with a metallic base layer in between, arediscussed. In order to confirm these effects, the impurity concentrationcontained in the Ar gas during the formation of the ferromagneticmetallic layer was varied within a range of 10 ppb-1 ppm, and filmformation was conducted. At this time, the impurity concentrationcontained in the Ar gas during formation of the metallic base layer wasfixed at 1.5 ppb.

Other points were identical to those in Embodiment 1.

In FIG. 5, the magnetic characteristics of the media produced are shownby a white circle. The horizontal axis in FIG. 5 indicates the oxygenconcentration in the CoNiCr film. The measurement of the oxygenconcentration was conducted by means of SIMS. The vertical axis in FIG.5 indicates the coercive force Hc in the circumferential direction ofthe sample at this time.

In the present Embodiment, as shown in FIG. 5, by keeping the oxygenconcentration in the CoNiCr film and the oxygen concentration in the Crfilm together at a level of 100 wtppm or less, an effect of a furtherincrease in the coercive force was obtained. It was separately observedthat the saturation magnetization values at this time were essentiallyconstant.

Accordingly, it was judged that if the oxygen concentration in theferromagnetic metallic layer and the oxygen concentration in themetallic base layer were together kept at a level of 100 wtppm or less,it was possible to increase the coercive force of the conventionalmedium by 100% or more (that is to say, to double it). Thus, it wasconfirmed that even though no Pt was contained in the magnetic layer, byreducing the oxygen concentration in the ferromagnetic metallic layerand the metallic base layer, it was possible to realize a medium whichwas sufficiently applicable to a high recording density.

(Embodiment 4)

In the present Embodiment, in place of the Co₆₂.5 --Ni₃₀ --Cr₇.5 ofEmbodiment 3, the following 5 types of alloys were employed as the Crgroup alloy target used for forming the ferromagnetic metallic layer:Co₈₅.5 --Cr₁₀.5 --Ta₄, Co₇₅ --Cr₁₃ --Pt₁₂, Co₇₀ --Ni₂₀ --Pt₁₀, Co₈₂.5--Ni₂₆ --Cr₇.5 --Ta₄, and Co₇₅.5 --Cr₁₀.5 --Ta₄ --Pt₁₀. Here, the numberfollowing each element indicates the proportion of that element in (at%).

Other points were identical to those shown in Embodiment 3.

In the present Embodiment, it was confirmed that irrespective of achange in the proportion of the elements comprising the Co group alloy,by maintaining the oxygen concentration present in the Co group alloyfilm and the oxygen concentration present in the Cr film together at alevel of 100 wtppm or less, the coercive force was increased by 50% ormore with all Co group alloys.

Accordingly, it was judged that the tendency for the coercive force toincrease when the oxygen concentration in the ferromagnetic metalliclayer and the oxygen concentration in the metallic base layer weretogether kept at a level of 100 wtppm or less was possible so long asthe target forming the ferromagnetic metallic layer was a Co groupalloy. In particular, when the Co₆₂.5 --Ni₃₀ --Cr₇.5 alloy, the Co₈₅.5--Cr₁₀.5 --Ta₄ alloy, or the Co₈₂.5 --Ni₂₆ --Cr₇.5 --Ta₄ alloy wasemployed, the coercive force was increased by 100% or more in comparisonwith the conventional medium, so that these alloys are preferablyemployed.

(Embodiment 5)

In the present Embodiment, the effects of a limitation of the thicknessof the metallic base layer in a magnetic recording medium in which aferromagnetic metallic layer is formed on the surface of a base bodywith a metallic base layer in between, are discussed. In order toconfirm these effects, the thickness of the metallic base layer wasvaried within a range of 0-100 nm, and film formation was conducted. Atthis time, a Co₈₅.5 --Cr₁₀.5 --Ta₄ alloy was employed as theferromagnetic metallic layer, and the thickness thereof was fixed at 40nm.

Other points were identical to those in Embodiment 3.

In FIG. 6, the magnetic characteristics of the media produced areindicated by white circles. The horizontal axis in FIG. 6 indicates thethickness of the metallic base layer comprising Cr. The vertical axis inFIG. 6 indicates the coercive force Hc in the circumferential directionof the sample at this time. Furthermore, as a comparative example, aconventional medium (in which the oxygen concentration in the CoCrTafilm and the oxygen concentration in the Cr film were both 260 wtppm)was evaluated in an identical manner. The results thereof are shown bythe black circles in FIG. 6.

It was determined from FIG. 6 that when the thickness of the Cr metallicbase layer was 2.5 nm or more, the coercive force of the medium of thepresent Embodiment had a value which was equal to or greater than themaximum value of the conventional medium. Furthermore, when thethickness of the Cr metallic base layer was 5 nm or more, a highcoercive force of 2000 Oe could be realized, so that this was furtherpreferable.

FIG. 7 shows the relationship between the thickness of the metallic baselayer comprising Cr and the noise N of the medium produced. In theFigure, the white circles indicate the media of the present Embodiment,while the black circles indicate a conventional medium.

Table 2 lists the evaluation methods and conditions for measuring thenoise described above. Solely the thickness of the Cr layer was madevariable within a range of 1 nm-100 nm, and other conditions were fixed.

                  TABLE 3                                                         ______________________________________                                        1. Measurement method                                                         Using the RWA501B produced by Guzik Co. and a spectral                        analyzer as the testing equipment for recording and playback,                 the level of medium noise was measured under the following                    measurement conditions.                                                       2. Measurement conditions                                                     Medium: Medium diameter and shape = 89 mm, disc-shaped                                Medium base body = NiP/Al                                                     Structure = C (20 nm)/CNiCr (40 nm)/Cr (d)/base body                          Thickness d of the Cr layer = 1 nm-100 nm                                     Product of the residual magnetic flux density and the                         thickness of the magnetic layer = 240 Gμm                                  Circumferential speed during disk rotation = 12 m/sec                 Head:   Type = Thin film head                                                         Pole length = 3.2 μm (both upper and lower parts)                          Gap length = 0.3 μm                                                        Track width = 6.0 μm                                                       Number of coil turns = 42 turns                                               Height above medium = 60 nm (from the surface of                              the medium)                                                           The medium noise N (unit: μVrms) was defined by the following              formula.                                                                       ##STR1##                                                                     ______________________________________                                    

From FIG. 7 it was determined that when the thickness of the Cr metallicbase layer was kept at a level of 100 nm or less, the noise of themedium of the present Embodiment had a value equal to or less theminimum value of the conventional medium. Furthermore, when thethickness of the Cr metallic base layer was 50 nm or less, a 10% orgreater reduction in medium noise could be realized, so that this wasfurther preferable.

Accordingly, in the present Embodiment, when the thickness of themetallic base layer comprising Cr was within a range of 2.5 nm-100 nm,media could be obtained which had higher coercive forces or lower levelsof medium noise in comparison with conventional media. Furthermore, whenthe thickness of the metallic base layer comprising Cr was restricted toa range of 5 nm-50 nm, a medium could be realized which was superiorwith respect to both coercive force and medium noise in comparison withthe conventional medium, so that this was further preferable.

(Embodiment 6)

In the present Embodiment, the effects of a restriction of the thicknessof the ferromagnetic metallic layer, in a magnetic recording medium inwhich a ferromagnetic metallic layer is formed on the surface of a basebody with a metallic base layer in between, will be discussed. In orderto confirm these effects, the thickness of the ferromagnetic metalliclayer was varied within a range of 1 nm-40 nm and and film formation wasconducted. At this time, the thickness of the metallic base layer wasfixed at 50 nm.

Other points were identical to those in Embodiment 3.

In FIG. 8, the magnetic characteristics of the media produced areindicated by white circles. The horizontal axis in FIG. 8 shows thethickness of the metallic base layer comprising CoCrTa. The verticalaxis in FIG. 8 indicates the coercive force Hc in the circumferentialdirection of the sample at this time. Furthermore, as a comparativeexample, a conventional medium (in which the oxygen concentration in theCoCrTa film was 260 wtppm) was similarly evaluated. The results thereofare shown by the black circles in FIG. 8.

It was determined from FIG. 8 that when the thickness of theferromagnetic metallic layer was within a range of 2.5 nm-40 nm, amedium could be obtained which had a higher coercive force than that ofthe conventional medium. Furthermore, when the thickness of theferromagnetic metallic layer was restricted to a range of 5 nm-20 nm, itwas possible to realize a coercive force of 2500 Oe or more.Conventionally, when the thickness of the ferromagnetic metallic layerwas reduced to 20 nm or less, a large scale reduction in coercive forcewas observed; however, by means of the present invention, a satisfactorycoercive force is obtainable at thicknesses of 20 nm or less, and it isthus possible to increase the freedom of medium design.

(Embodiment 7)

In the present Embodiment, the effects of a restriction in the oxygenconcentration contained in the ferromagnetic metallic layer, in amagnetic recording medium in which a ferromagnetic metallic layer isformed on the surface of a base body, will be discussed. In order toconfirm these effects, the impurity concentration contained in the Argas during the formation of a ferromagnetic metallic layer was variedwithin a range of 10 ppb-1 ppm, and film formation was conducted.

The sputtering apparatus used in the production of the medium in thepresent Embodiment was a magnetron sputtering apparatus (model numberILC3013: load-lock style stationary opposition type) produced by AnerubaCo., as in Embodiment 1. Table 3 shows the film formationcharacteristics during the production of the magnetic recording mediumin the present Embodiment.

                  TABLE 4                                                         ______________________________________                                        ITEM              SET VALUES                                                  ______________________________________                                         1! Base Body material                                                                          Al-Mg alloy (provided with a                                                  10 m thick (Ni-P) plated film)                               2! Base Body diameter and                                                                      89 mm, disc-shaped                                          shape                                                                          3! Base Body surface form                                                                      Textured, Ra = 5 nm                                          4! Attained vacuum degree                                                                      5 × 10.sup.-7 (same in all chambers)                  (Torr)                                                                         5! Impurity concentration in                                                                   10 ppb - 1 ppm (film formation                              the Ar gas        chamber 1)                                                   6! Ar gas pressure (mTorr)                                                                     2 (film formation chamber 1)                                 7! Base Body surface                                                                           230 (same in all chambers)                                  temperature maintained (°C.)                                            8! Target material (at %)                                                                      Co.sub.85 Cr.sub.15                                          9! Target diameter (inch)                                                                      6                                                            10! Impurity concentration in                                                                  20                                                          target (ppm)                                                                   11! Distance between target                                                                    35                                                          and base body (mm)                                                             12! Power applied to target                                                                    Direct current, 200                                         (W)                                                                            13! Direct current bias                                                                        300                                                         applied to base body during                                                   film formation (-Volt)                                                         14! Film thickness produced                                                                    100                                                         (nm)                                                                          ______________________________________                                    

Hereinbelow, the steps involved in the production method for magneticrecording media in accordance with the present Embodiment will beexplained in order. The numbers in parentheses below indicate thisorder.

(1) An aluminum alloy substrate having a disk shape, such that the innerand outer diameters were 25 mm and 89 nm respectively, and the thicknesswas 1.27 nm, was used as the base body. A (Ni--P) film having athickness of 10 μm was provided on the surface of the aluminum alloysubstrate by means of a plating method. Slight concentric scratches(texture) were provided in the surface of the (Ni--P) film by means of amechanical method, and the surface roughness of the base body whenscanned in the radial direction of the disk was such that the averagecenter line roughness Ra was 5 nm.

(2) The base body described above was subjected, prior to the filmformation described below, to a cleaning process using mechanical andchemical methods, and to a drying process using hot air and the like.

(3) When the drying process described above was complete, the base bodywas set in a base body holder, the material of which was aluminum, whichwas placed in the load chamber of the sputtering apparatus. After theinterior of the load chamber was evacuated to an attained vacuum degreeof 3×10⁻⁹ Torr using a vacuum exhaust apparatus, a heating process wasconducted with respect to the base body at a temperature of 230° C. andfor a period of 5 minutes and using an infrared lamp.

(4) The base body holder was then moved from the load chamber to filmformation chamber 1 for CoCr film production. After being moved, thebase body was maintained at a temperature of 230° C. using an infraredlamp. Film formation chamber 1 was evacuated in advance to an attainedvacuum degree of 3×10⁻⁹ Torr, and after the base body holder was moved,the door valve between the load chamber and the film formation chamber 1was closed. The impurity concentration of the CoCr target which was usedwas 20 ppm.

(5) Ar gas was introduced into film formation chamber 1, and the gaspressure within film formation chamber 1 was set to 2 mTorr. Theimpurity concentration contained in the Ar gas which was employed wasvaried within a range of 10 ppb-1 ppm.

(6) A voltage of 200 W was applied to the CoCr target from a directcurrent power source, and a plasma was generated. As a result, the CoCrtarget was caused to sputter, and a CoCr layer having a thickness of 100nm was formed on the surface of the base body, which was placed in aposition of parallel opposition to the target.

(7) After the formation of the CoCr layer, the base body holder wasmoved from film formation chamber 1 to the extraction chamber. Afterthis, N₂ gas was introduced into the extraction chamber, and once thepressure within was returned to atmospheric pressure, the base body wasremoved. By means of processes (1)-(6) described above, a magneticrecording medium having a CoCr/NiP/Al structure was produced.

A target was used in which the presence of impurities was strictlysuppressed. The composition of the target used was as follows: 85 at %Co and 15 at % Cr, and the impurity concentration of the target was 20ppm. The impurities were as follows: Fe:27, Si<10, Al<10, C:30, O:20,N>10 (wtppm).

In FIG. 9, the magnetic characteristics of the media produced areindicated by a white circle. The horizontal axis in FIG. 9 indicates theoxygen concentration within the CoNiCr film. The measurement of theoxygen concentration was conducted by means of SIMS. The vertical axisin FIG. 9 indicates the coercive force Hc in the circumferentialdirection of the sample at this time.

Conventionally, the impurity concentration present in the Ar gas usedduring the formation of a ferromagnetic metallic layer comprising CoCrwas 1 ppm. Furthermore, the oxygen concentration in the CoCr film of aconventional medium was 260 wtppm, and the coercive force of aconventional medium is indicated in FIG. 9 by a black circle.

In the present Embodiment, as shown in FIG. 9, by keeping the oxygenconcentration in the CoCr film at a level of 100 wtppm or less, aneffect of a great increase in the coercive force in a directionperpendicular to the film surface was obtained. It was separatelyobserved that the saturation magnetization values at this time wereessentially constant.

Accordingly, if the oxygen concentration of the ferromagnetic metalliclayer is kept at a level of 100 wtppm or less, it is possible to realizean increase of 20% or more in the coercive force obtained when theoxygen concentration in a conventional ferromagnetic metallic layercomprising CoCr was 260 wtppm. That is to say, by reducing the oxygenconcentration in the ferromagnetic metallic layer, it was confirmed thatit was possible to realize a medium which was applicable to highrecording densities.

Furthermore, in the present Embodiment, the case was described in which,in a magnetic recording medium in which a ferromagnetic metallic layerwas formed on the surface of a base body, the ferromagnetic metalliclayer comprised CoCr; however, the same trends were confirmed when theferromagnetic metallic layer comprised CoCrTa and CoPt.

Furthermore, even in the case in which the ferromagnetic metallic layerwas provided on the surface of the base body with a soft magnetic film,for example, NiFe, CoZrNb, or the like, in between, identical effectswere obtained.

In the Embodiments above, a Ni--P/Al substrate was employed as the basebody; however, it was confirmed that the present invention is effectiveeven when a non-magnetic layer was provided on the surface of the basebody, for example, when a glass substrate having Ti, C, or the likeformed thereon was employed.

(Embodiment 8)

In the present Embodiment, the effects of a reduction in the normalizedcoercive force (expressed by Hc/Hk^(grain)), in a magnetic recordingmedium in which a ferromagnetic metallic layer is formed on the surfaceof the base body with a metallic base layer in between, are discussed.In order to confirm these effects, the impurity concentration containedin the Ar gas during the formation of both the ferromagnetic metalliclayer and the metallic base layer was varied within a range of 10 ppb to1 ppm, and film formation was conducted. At this time, the material usedfor the metallic base layer was Cr, and the thickness thereof was fixedat 50 nm. Furthermore, six types of Co group alloy were used for theferromagnetic metallic layer, and the thickness thereof was fixed at 40nm. The six types of Co group alloy were: Co₆₂.5 --Ni₃₀ --Cr₇.5, Co₈₅.5--Cr₁₀.5 --Ta₄, Co₇₅ --Cr₁₃ --Pt₁₂, Co₇₀ --Ni₂₀ --Pt₁₀, Co₈₂.5 --Ni₂₆--Cr₇.5 --Ta₄, and Co₇₅.5 --Cr₁₀.5 --Ta₄ --Pt₁₀. Here, the numbersfollowing each element indicate the proportion of that element in (at%).

Other points were identical to those of Embodiment 3.

In FIG. 10, the magnetic characteristics of the media produced areindicated by a white circle. The horizontal axis in FIG. 10 indicatesthe normalized coercive force (Hc/Hk^(grain)), and the vertical axis inFIG. 10 indicates the level of noise N in the media produced. Themeasurement method and conditions for the level of medium noise wereidentical to those in Embodiment 5. Furthermore as a comparativeexample, an identical evaluation was conducted with respect to aconventional medium (in which the oxygen concentration in theferromagnetic metallic layer was 260 wtppm). The results thereof areshown by the black circles in FIG. 10.

The values of the normalized coercive force for each Co alloy shown inFIG. 10 are listed in Table 4.

                  TABLE 5                                                         ______________________________________                                                      Normalized coercive                                                                        Normalized coercive                                              force in the present                                                                       force in the                                       Composition (at %)                                                                          Embodiment   Comparative Example                                ______________________________________                                        Co.sub.62.5 --Ni.sub.30 --Cr.sub.7.5                                                        0.40         0.18                                               Co.sub.85.5 --Cr.sub.10.5 --Ta.sub.4                                                        0.42         0.28                                               Co.sub.75 --Cr.sub.13 --Pt.sub.12                                                           0.38         0.19                                               Co.sub.70 --Ni.sub.20 --Pt.sub.10                                                           0.35         0.20                                               Co.sub.82.5 --Ni.sub.26 --Cr.sub.7.5 --Ta.sub.4                                             0.41         0.24                                               Co.sub.75.5 --Cr.sub.10.5 --Ta.sub.4 --Pt.sub.10                                            0.38         0.25                                               ______________________________________                                    

It was determined from FIG. 10 that irrespective of the material usedfor the ferromagnetic metallic layer, the media of the presentEmbodiment possessed a high normalized coercive force of 0.3 or more, incomparison to the normalized coercive force of the conventional media,which were less than 0.3. Furthermore, with respect to the level ofmedium noise, this level was lower in all the media in accordance withthe present Embodiment than in the conventional media. Incidentally, theupper limit of the normalized coercive force is theoretically indicatedto be 0.5 when the crystal grains are completely isolated; however, insystems such as thin films having some random portions, this value issmaller than 0.5.

Accordingly, by means of restricting the normalized coercive force(Hc/Hk^(grain)) of the ferromagnetic metallic layer to a range from 0.3to less than 0.5, it was confirmed that it is possible to realize amedium having a low level of noise which is applicable to high recordingdensities.

In the Embodiment given above, a Ni--P/Al substrate was employed as thebase body; however, it is also possible to use Al, glass, Si, Ti, C,ceramics, plastics, resins, and any one of these having metallic filmsor insulating films formed thereon.

(Embodiment 9)

In the present Embodiment, the effects of a restriction, to a level of10 ppb or less and a level of 100 ppt or less, of the impurityconcentration in the Ar gas used in film formation, in a manufacturingmethod for magnetic recording media in which a metallic base layer andferromagnetic metallic layer are successively formed on the surface of abase body by means of a sputtering method, will be explained. In orderto confirm these effects, the impurity concentrations contained in theAr gas during formation of the ferromagnetic metallic layer and themetallic base layer were varied within a range of 10 ppt-10 ppm, andfilm formation was conducted.

Other points were identical to those in Embodiment 3.

In FIG. 11, the magnetic characteristics of the media produced areindicated by white circles. The horizontal axis in FIG. 11 indicates theimpurity concentration contained in the Ar gas during the formation ofthe ferromagnetic metallic layer and the metallic base layer, while thevertical axis in FIG. 11 indicates the coercive force Hc in thecircumferential direction of the sample at this time. Furthermore, theresults obtained with respect to a conventional medium are indicatedwith black circles, as a conventional example. The impurityconcentration contained in the Ar gas used in the production of aconventional medium is 1 ppm or more.

It was determined from FIG. 11 that when the impurity concentrationcontained in the Ar gas was kept at 10 ppb or less, it was possible toobtain a medium having a coercive force which was 30% or more higherthan that conventionally obtainable. Furthermore, when the impurityconcentration contained in the Ar gas was kept at a level of 100 ppt orless, it was possible to realize a coercive force which was 50% or morehigher than that conventionally obtainable, so that this is furtherpreferable.

Furthermore, it was separately confirmed that the above effects wereobtainable even when a Co group alloy layer was directly formed on thesurface of the base body without an intervening metallic base layer.

(Embodiment 10)

In the present Embodiment, the effects of conducting cleaning processingwith respect to the surface of the base body prior to forming themetallic base layer will be discussed. The cleaning method employed toconfirm these effects, and the order thereof, are as given below.

(1) The base body comprising an aluminum alloy substrate which wasemployed in Embodiment 3 was first placed within a cleaning chamber, andthis chamber was then evacuated to a vacuum degree of 6×10⁻⁷ Torr.

(2) The base body was heated for a period of 5 minutes using an infraredlamp so that the surface temperature thereof reached 230° C.

(3) Ar gas having an impurity concentration of 10 ppb was introducedinto the cleaning chamber, and the gas pressure was set at 1 mTorr.

(4) A voltage was applied to the base body from an RF power source, anda cleaning process was conducted. The conditions of this were such thatthe power density was 2.5 W/cm², and the cleaning rate was 0.013 nm/sec;by altering the cleaning period, the amount which was stripped wasvaried within a range of 0.2-4 nm.

(5) After this, a Cr film was formed as a metallic base layer on thesurface of the base body, a CoNiCr film was formed as a ferromagneticmetallic layer, and a C film was formed as a protective layer. The filmformation conditions thereof were identical to those given in Embodiment3.

In FIG. 12, the relationship between the amount stripped from the basebody surface by means of the cleaning described above and the coerciveforce of the media produced is shown. The horizontal axis shows thecleaning time with respect to the surface of the (Ni--P) layer; 130seconds corresponds to an amount stripped of 2.4 nm. The vertical axisindicates the coercive force of the medium at this time; Hc (cir)indicates the coercive force of the disc shaped base body in thecircumferential direction, while Hc (rad) shows the coercive force inthe radial direction, and these are represented by, respectively, whitecircles and white squares. Furthermore, as a comparative example, thecoercive forces of media which were subjected to cleaning using Ar gashaving an impurity concentration of 20 ppb are indicated by blackcircles and black squares.

As shown in FIG. 12, when the amount stripped from the base body surfaceby means of the cleaning process was within a range of 0.2 nm-1.0 nm,the coercive force increased in the circumferential direction and theradial direction, and furthermore, it was also possible to alter theratio Hc(cir)/Hc(rad) of the coercive forces. It was determined that arange of 0.3 nm-0.6 nm was particularly advantageous for this increasein the coercive force.

FIG. 13 shows the results of an X-ray diffraction of each medium surfaceat this time; it indicates that the crystalline structure of the Cr baselayer and the crystalline structure of the Co alloy layer thereon arealtered by the cleaning process, and if the amount stripped is toogreat, the diffraction peaks of Cr (200) and CoNiCr (110) disappear.

Accordingly, it was determined that conducting a cleaning process whichstrips the appropriate amount from the surface of the base body prior toformation of a metallic base layer is effective in the realization of ahigh coercive force. This effect was also confirmed with other Co groupalloys, for example Co₈₅.5 --Cr₁₀.5 --Ta₄, Co₇₅ --Cr₁₃ --Pt₁₂, Co₇₀--Ni₂₀ --Pt₁₀, Co₈₂.5 --Ni₂₆ --Cr₇.5 --Ta₄, and Co₇₅.5 --Cr₁₀.5 --Ta₄--Pt₁₀. Here, the numbers following each element indicate the proportionof that element in (at %). Furthermore, it was separately confirmed thatthe effects described above were also obtainable when a Co group alloylayer was provided directly on the surface of the base body without ametallic base layer in between.

(Embodiment 11)

In the present Embodiment, the effects of a restriction of the impurityconcentration of the target used in the formation of the metallic baselayer to a level of 150 ppm or less will be discussed. In order toconfirm the effects, the impurity concentration contained in the targetused in the formation of a metallic base layer comprising Cr was variedwithin a range of 50 ppm-300 ppm, and film formation was conducted. Atthis time, the impurity concentration in the CoNiCr target which wasused to form the ferromagnetic metallic layer was 20 ppm. Furthermore,the impurity concentration in the Ar gas used during the formation ofthe metallic base layer and the ferromagnetic metallic layer was 1.5ppb.

Other points were identical to those in Embodiment 19.

In FIG. 14, the relationship between the impurity concentration in thetarget used during the formation of the metallic base layer and thecoercive force of the media produced is shown. The vertical axis showsthe values of the coercive force in the circumferential direction of thedisc shaped base bodies.

As shown in FIG. 14, it was determined that when the impurityconcentration in the target used during the formation of the metallicbase layer was kept at 150 ppm or less, the coercive force of the mediadramatically increased.

(Embodiment 12)

In the present Embodiment, the effects of a restriction of the impurityconcentration in the target used during the formation of theferromagnetic metallic layer to a level of 30 ppm or less will bediscussed. In order to confirm the effect, Co₈₅.5 --Cr₁₀.5 --Ta₄ wasused as the target during the formation of the ferromagnetic metalliclayer, and the impurity concentration contained in this target wasvaried within a range of 5 ppm-200 ppm, and film formation wasconducted. At this time, the impurity concentration in the Cr targetused to form the metallic base layer was 120 ppm. Furthermore, theimpurity concentration in the Ar gas which was used during the formationof the metallic base layer and the ferromagnetic metallic layer was 1.5ppb.

Other points were identical to those in Embodiment 19.

In FIG. 15, the relationship between the impurity concentration of thetarget used during the formation of the ferromagnetic metallic layer andthe coercive force of the media produced is shown. The vertical axisindicates the values of the coercive force of the disc shaped basebodies in the circumferential direction.

As shown in FIG. 15, it was determined that when the impurityconcentration of the target used during the formation of theferromagnetic metallic layer was kept at 30 ppm or less, the coerciveforce of the media dramatically increased.

(Embodiment 13)

In the present Embodiment, the effects of applying a negative bias tothe base body during the formation of the metallic base layer and/or theferromagnetic metallic layer will be discussed. In order to confirmthese effects, the value of the applied bias mentioned above was variedwithin a range of 0--500V, and film formation was conducted.Furthermore, 3 combinations of layers were executed while applying abias (only a metallic base layer, only a ferromagnetic metallic layer,and both a metallic base layer and a ferromagnetic metallic layer). Atthis time, the impurity concentration in the Cr target used to form themetallic base layer was 120 ppm and the impurity concentration in theCoNiCr target used to form the ferromagnetic metallic layer was 20 ppm.Furthermore, the impurity concentration in the Ar gas used during theformation of the metallic base layer and the ferromagnetic metalliclayer was 1.5 ppb.

Other points were identical to those in Embodiment 19.

In FIG. 16, the relationship between the negative bias applied to thebase body and the coercive force of the media produced is shown. Thevertical axis indicates the values of the coercive force of the discshaped base bodies in the circumferential direction using white circles.Furthermore, an identical evaluation was conducted with respect to aconventional medium (in which both the oxygen concentration in theCoNiCr film and the oxygen concentration in the Cr film were 260 wtppm)as a comparative example. These results are shown in FIG. 16 by blackcircles.

As shown in FIG. 16, the coercive force of the medium increased evenwhen a bias was applied only during the formation of one or the otherlayers; however, when a bias was applied during the formation of bothlayers, the coercive force was further increased, so that this morepreferable. Furthermore, it was determined that if the applied biasvalue is restricted to a range of -100V--400V, an increase of 10% ormore in the coercive force can be realized in comparison to the case inwhich a bias is not applied.

(Embodiment 14)

In the present Embodiment, the effects of setting the vacuum degreeattained in the film formation chambers in which the metallic base layerand/or the ferromagnetic metallic layer is formed to a level of 8×10⁻⁸Torr or less will be discussed. In order to confirm these effects, thevalue of the attained vacuum degree in the film formation chambers usedfor the formation of the metallic base layer and the ferromagneticmetallic layer was varied within a range of 3×10⁻⁹ Torr-5×10⁻⁷ Torr, andfilm formation was conducted. At this time, the impurity concentrationin the Cr target used for the formation of the metallic base layer was120 ppm, and the impurity concentration in the CoNiCr target used in theformation of the ferromagnetic metallic layer was 20 ppm. Furthermore,the impurity concentration in the Ar gas used during the formation ofthe metallic base layer and the ferromagnetic metallic layer was 1.5ppb.

Other points were identical to those in Embodiment 19.

In FIG. 17, the relationship between the attained vacuum degree in thefilm formation chambers used for the formation of the metallic baselayer and ferromagnetic metallic layer, and the coercive force of themedia produced, is shown. The vertical axis indicates the values of thecoercive force of the disc shaped base bodies in the circumferentialdirection.

As shown in FIG. 17, when the attained vacuum degree was 8×10⁻⁸ Torr orless, the coercive force increased dramatically. Furthermore, at levelsof 5×10⁻⁸ Torr or less, a high coercive force of 2000 Oe or more wasobtainable, so that this is further preferable.

Furthermore, it was separately confirmed that even when only either theattained vacuum degree in the film formation chamber used for formationof the metallic base layer or that in the film formation chamber usedfor the ferromagnetic metallic layer was 8×10⁻⁸ Torr or less, thecoercive force increased.

(Embodiment 15)

In the present Embodiment, the effects of maintaining the surfacetemperature of the base body during the formation of the metallic baselayer and/or the ferromagnetic metallic layer within a range of 60°C.-150° C. will be discussed. In order to confirm these effects, thesurface temperature of the base body during the formation of themetallic base layer and the ferromagnetic metallic layer was variedwithin a range of 25° C.-250° C., and film formation was conducted. Atthis time, the impurity concentration in the Cr target used to form themetallic base layer was 120 ppm, and the impurity concentration in theCoNiCr target used to form the ferromagnetic metallic layer was 20 ppm.Furthermore, the impurity concentration in the Ar gas used during theformation of the metallic base layer and the ferromagnetic metalliclayer was 1.5 ppb. A textured Ni--P/Al substrate having a surfaceroughness Ra of 0.7 nm was used as the base body.

Other points were identical to those in Embodiment 19.

In FIG. 18, the relationship between the surface temperature of the basebody during the formation of the metallic base layer and/orferromagnetic metallic layer, and the coercive force of the mediaproduced, is shown. The vertical axis indicates the values of thecoercive force of the disc shaped base bodies in the circumferentialdirection, using white circles. Furthermore, as comparative examples,the coercive forces in the case in which the impurity concentration ofthe Ar gas used during the formation of the metallic base layer andferromagnetic metallic layer was 20 ppb are shown using black circles.

FIG. 19 shows the relationship between the surface temperature of thebase body during the formation of the metallic base layer and/orferromagnetic metallic layer and the surface roughness Ra of the mediaproduced.

As shown in FIG. 18, when the surface temperature was set to 60° C. ormore, a coercive force higher than that of conventional media wasattained. On the other hand, as shown in FIG. 19, at temperatures of150° C. or more, the surface roughness Ra of the media increased. Whenan experiment was conducted in which the height at which the magnetichead rode above such base bodies was 15 nm, there were numerousoccurrences of a phenomenon in which the magnetic head collided with thesurface of the medium, that is to say, there were numerous head crashes.Furthermore, when the surface temperature of the base body during theformation of the metallic base layer or the ferromagnetic metallic layerwas set within a range of 60° C.-150° C., no head crashes occurred.

Accordingly, it was determined that in order to simultaneously realizehigher coercive forces than those conventionally obtainable and a lowmagnetic head height of 15 nm or less, it was necessary to set thesurface temperature of the base body during the formation of themetallic base layer and/or ferromagnetic metallic layer to within arange of 60° C.-150° C.

Furthermore, since it is possible to produce media at low temperaturesat which high coercive forces were conventionally unobtainable, basebodies which could not be used because gas was released from the basebodies as a result of heating, such as ceramics, plastics, resins, andthe like, can be employed.

In the above embodiments, a Ni--P/Al substrate was used as the basebodies; however, it was confirmed that the present invention was alsoeffective when a non-magnetic layer was provided on the surface of thebase body, for example when a glass substrate having Ti, C, or the likeformed thereon was employed.

(Embodiment 16)

In the present Embodiment, the effects of limiting the surface roughnessRa of the base body to a level of 3 nm or less, or a level of 1 nm orless, will be discussed. In order to confirm these effects, the surfaceroughness was varied within a range of 0.5 nm-7 nm, and film formationwas conducted. At this time, the impurity concentration of the Cr targetused for forming the metallic base layer was 120 ppm, and the impurityconcentration of the CoNiCr target used for forming the ferromagneticmetallic layer was 20 ppm. Furthermore, the impurity concentration ofthe Ar gas used during the formation of the metallic base layer and theferromagnetic metallic layer was 1.5 ppb.

Other points were identical to those in Embodiment 19.

In FIG. 20, the relationship between the surface roughness Ra of thebase body and the coercive force of the media produced is shown. Thevertical axis indicates the coercive force values of the disc shapedbase bodies in the circumferential direction using white circles.Furthermore, as a conventional example, the coercive forces obtained inthe case in which the impurity concentration of the Ar gas used duringthe formation of the metallic base layer and the ferromagnetic metalliclayers was 20 ppb are also indicated by black circles.

As shown in FIG. 20, by limiting the surface roughness Ra of the basebody to 3 nm or less, a 30% increase in coercive force was obtained.Furthermore, when Ra was 1 nm or less, a further increase in coerciveforce was obtained, so that this was more preferable. On the other hand,in the conventional medium, when Ra decreased, there was a precipitousdecline in coercive force.

Accordingly, in the present Embodiment, it is possible to simultaneouslyachieve a small Ra value which permits the realization of a low magnetichead height, and a high coercive force, so that a medium can be obtainedwhich is suitable for application to high recording densities.

(Embodiment 17)

In the present Embodiment, the effects of employing (Ar+N₂) or (Ar+H₂)gas in place of Ar as the gas which is used during the formation of themetallic base layer and/or the ferromagnetic metallic layer will bediscussed. At this time, the impurity concentration of the Cr targetused for forming the metallic base layer was 120 ppm, and the impurityconcentration of the CoNiCr target used for forming the ferromagneticmetallic layer was 20 ppm. Furthermore, the impurity concentration ofthe Ar gas used during the formation of the metallic base layer and theferromagnetic metallic layer was 1.5 ppb.

Other points were identical to those in Embodiment 19.

In FIG. 21, the relationship between the proportion of N₂ gas in the(Ar+N₂) gas and the coercive force of the media produced is shown bywhite circles. In FIG. 22, the relationship between the proportion of N₂gas in the (Ar+H₂) gas and the coercive force of the media produced isshown by white circles. Furthermore, as a comparative example, identicalevaluations were performed with respect to conventional media (in whichthe oxygen concentration in the CoNiCr layer and the oxygenconcentration in the Cr layer were both 260 wtppm). The results thereofare shown by the black circles in FIGS. 21 and 22.

As shown in FIG. 21, when the proportion of N₂ gas in the (Ar+N₂) gaswas 0.05 or less, a higher coercive force was obtained than when Ar gasalone was used. Furthermore, as shown in FIG. 22, when the proportion ofH₂ gas in the (Ar+H₂) gas was 0.03 or less, a higher coercive force wasobtained than when Ar gas alone was used.

Accordingly, by using a mixture of at least one of N₂ gas and H₂ gaswith Ar gas as the gas used during the formation of the metallic baselayer and/or ferromagnetic metallic layer, it is possible to realize amedium having a high coercive force which is applicable to highrecording densities.

Industrial Applicability

By means of the magnetic recording medium in accordance with the presentinvention, it is possible to realize a high coercive force and low levelof medium noise, and it is possible to provide a magnetic recordingmedium which is applicable to high recording densities.

By means of the manufacturing method for magnetic recording media inaccordance with the present invention, the degree of magnetic isolationof the crystalline grains in the ferromagnetic metallic film isincreased, and it is possible to increase the coercive force.Furthermore, since the level of medium noise is also reduced, recordingand playback characteristics are improved. Furthermore, since it ispossible to produce the media using low cost materials in which no Pt iscontained in the ferromagnetic metallic film, and by means of processeshaving high productivity, it is possible to greatly reduce the costsassociated with magnetic recording media applicable to high recordingdensities.

I claim:
 1. A magnetic recording medium wherein a ferromagnetic metalliclayer is formed on a surface of a base body with a metallic base layerin between, which employs reversal of magnetization, characterized inthat an oxygen concentration within crystal grains of said ferromagneticlayer is 100 wtppm or less.
 2. A magnetic recording medium wherein aferromagnetic metallic layer is formed on a surface of a base body witha metallic base layer in between, which employs reversal ofmagnetization, characterized in that an oxygen concentration withincrystal grains of said metallic base layer is 100 wtppm or less.
 3. Amagnetic recording medium in accordance with claim 2, characterized inthat the oxygen concentration in said ferromagnetic metallic layer is100 wtppm or less.
 4. A magnetic recording medium in accordance withclaim 1, characterized in that said ferromagnetic metallic layercomprises a Co group alloy.
 5. A magnetic recording medium in accordancewith claim 4, characterized in that said Co group alloy comprises oneselected from a group containing CoNiCr, CoCrTa, CoPtCr, CoPtNi,CoNiCrTa, and CoCrPtTa.
 6. A magnetic recording medium in accordancewith claim 1, characterized in that said metallic base layer comprisesCr.
 7. A magnetic recording medium in accordance with claim 1,characterized in that the thickness of said metallic base layer iswithin a range of 2.5 nm-100 nm.
 8. A magnetic recording medium inaccordance with claim 1, characterized in that the thickness of saidmetallic base layer is within a range of 5 nm-30 nm.
 9. A magneticrecording medium in accordance with claim 1, characterized in that thethickness of said ferromagnetic metallic layer is within a range of 2.5nm-40 nm.
 10. A magnetic recording medium in accordance with claim 1,characterized in that the thickness of said ferromagnetic metallic layeris within a range of 5 nm-20 nm.
 11. A magnetic recording medium,wherein a ferromagnetic metallic layer is formed on a surface of a basebody, which employs reversal of magnetization, characterized in that anoxygen concentration within crystal grains of said ferromagneticmetallic layer is 100 wtppm or less.
 12. A magnetic recording medium inaccordance with claim 11, characterized in that said ferromagneticmetallic layer comprises a Co group alloy.
 13. A magnetic recordingmedium in accordance with claim 12, characterized in that said Co groupalloy is selected from a group containing CoCr, CoCrTa, and CoPt.
 14. Amagnetic recording medium in accordance with claim 1, characterized inthat a non-metallic layer is formed on the surface of said base body.15. A magnetic recording medium in accordance with claim 1,characterized in that a normalized coercive force, expressed byHc/Hk^(grain), of said ferromagnetic metallic layer is greater than orequal to 0.3 and less than 0.5.
 16. A magnetic recording medium inaccordance with claim 1, characterized in that said base body comprisesAl alloy.
 17. A magnetic recording medium in accordance with claim 1,characterized in that said base body comprises glass.
 18. A magneticrecording medium in accordance with claim 1, characterized in that saidbase body comprises silicon.
 19. A manufacturing method for magneticrecording media, wherein a metallic base layer and a ferromagneticmetallic layer are successively formed on a surface of a base body by asputtering method, characterized in that Ar gas used in film formationhas an impurity concentration of 10 ppb or less.
 20. A manufacturingmethod for magnetic recording media in accordance with claim 19,characterized in that the impurity concentration of said Ar gas used infilm formation is 100 ppt or less.
 21. A manufacturing method formagnetic recording media in accordance with claim 19, characterized inthat, prior to the formation of said metallic base layer, the surface ofsaid base body is subjected to a cleaning process by a high-frequencysputtering method employing Ar gas having an impurity concentration of10 ppb or less, and the surface of said base body is removed to a depthof 0.2 nm-1 nm.
 22. A manufacturing method for magnetic recording mediain accordance with claim 19, characterized in that said metallic baselayer comprises Cr, and the impurity concentration in a target employedduring the formation of said metallic base layer is 150 ppm or less. 23.A manufacturing method for magnetic recording media, wherein aferromagnetic metallic layer is formed on a surface of a base body by asputtering method, characterized in that Ar gas used in film formationhas an impurity concentration of 10 ppb or less.
 24. A manufacturingmethod for magnetic recording media in accordance with claim 23,characterized in that the impurity concentration of said Ar gas is 100ppt or less.
 25. A manufacturing method for magnetic recording media inaccordance with claim 23, characterized in that, prior to the formationof said ferromagnetic metallic layer, the surface of said base body issubjected to a cleaning process by means of a high frequency sputteringmethod, and the surface of said base body is removed to a depth of 0.2nm-1 nm.
 26. A manufacturing method for magnetic recording media inaccordance with claim 19, characterized in that the impurityconcentration of a target used in the formation of said ferromagneticmetallic layer is 30 ppm or less.
 27. A manufacturing method formagnetic recording media in accordance with claim 19, characterized inthat during the formation of said metallic base layer and/orferromagnetic metallic layer, a negative bias is applied to said basebody.
 28. A manufacturing method for magnetic recording media inaccordance with claim 19, characterized in that said negative bias iswithin a range of -100V--400V.
 29. A manufacturing method for magneticrecording media in accordance with claim 19, characterized in that theattained vacuum degree in film formation chambers used for forming saidmetallic base layer and/or ferromagnetic metallic layer is 8×10⁻⁸ Torror less.
 30. A manufacturing method for magnetic recording media inaccordance with claim 19, characterized in that the surface temperatureof said base body during formation of said metallic base layer and/orferromagnetic metallic layer is within a range of 60° C.-150° C.
 31. Amanufacturing method for magnetic recording media in accordance withclaim 19, characterized in that said base body has a non-magnetic layerformed on the surface thereof.
 32. A manufacturing method for magneticrecording media in accordance with claim 19, characterized in that thesurface roughness of said base body is such that Ra is 3 nm or less. 33.A manufacturing method for magnetic recording media in accordance withclaim 19, characterized in that the surface roughness of said base bodyis such that Ra is 1 nm or less.
 34. A manufacturing method for magneticrecording media in accordance with claim 19, characterized in that a gasused during formation of said metallic base layer and/or ferromagneticmetallic layer comprises a mixture of at least one of N₂ gas and H₂ gaswith Ar gas.